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Influence of peak overload or variable loading sequences on fatigue-crack propagation in 18Cr10Ni stainless steel
these structures requiree evaluation of stress concentration factors (SCFs) and fatigue strength of the tubular joints. The radial flexibility of the chord is the main parameter affecting the stress concentration around intersection of chord and brace tubes. Among the different methods available to reduce stress concentration at the intersection, provision of intemel ring stiffeners is often preferred for its advantages, Tests were conducted on stiffened and unstiffened tubular Y joints to investigate the effect of internal dng stiffeners on SCF. The experimental values of SCF are compared with the parametric formulae recommended by the Underwater Engineering Group (UEG) for stiffened and unstiffened tubular joints. Fatigue tests on stiffened tubular joints under axial and moment loads were conducted. The experimental fatigue teat results are compared with the recommendations made by the various coding authorities: DnV, API, UEG, and NPO. Results of the experimental investigations are presented. The effect of ring stiffeners on the static and fatigue beheviour of tubular welded Y joints under axial and moment loads is examined.
High tamporaturo, l o w cycle f a t i g u e b e h e v l o u r o f AISI Type 316LN base metal, 316LN-316 w e l d j o i n t and 316 all-weld metal. Valsan, M., Sankara
Reo, K.B., Sandhya, R. and Mannan, S.L. Mater. Sci. Eng. A Jan. 1992 A14S, (2), L9-L12 Studies on the strein-controlled low cycle fatigue (LCF) behaviour of type 316LN stainless steel (SS) base material, type 316 SS all-weld metal and 316LN-316 weldments prepared by the shielded metal arc welding (SMAW) process at 837 K have been conducted at a strain rate of 3 x 10-3 s -1. The results indicated that the LCF resistance of all-weld metal was better than that of the base material while weldments displayed the least fatigue resistance. The better fatigue resistance of the all-weld metal has been attributed to the beneficial effects associated with fine distribution of ;~-ferrite in the auatenite matrix while the poor fatigue resistance of the weldment has been ascribed to the detrimental effects associated with coarse grain size and surface intergrenular cracking in the heet-affected zone. The cyclic stress amplitude varied with the material condition and strain amplitude in the LCF test. Graphs, photomicrographs. 9 refs.
Roiled a l u m i n l u m alloy adapted f o r superplaatic forming and method for making. Komatsubara, T., Tagata, 7". and Matsuo, M. UK Patent 2245592 8 Jan. 1992 Provided is a superplastic forming AI alloy in rolled form which exhibits superplaaticity and has improved corrosion resistance, weldability, and strength and fatigue property after auperplaatic forming, eliminating a need for heat treatment after superplaatic forming. Preferred alloys have an excellent outer appearance of grey to black colour after anodization. The alloy consists essentially of, in wt.%, 2.0-8.0% magnesium, 0.3-1.5% Mn, 0.0001-0.01% beryllium, an optional element selected from Cr, vanadium, and Zr, an optional grain refining agent of Ti or Ti and boron, <0.2% Fe and <0.1% Si as impurities, and the balance of AI, wherein intermatallic compounds have s size of up to 20 I~m, and the content of hydrogen present is up to 0.35 cm 3/100 g. Particularly when a minor amount of Ti or Ti and B grain refining agent is contained, Mn precipitates have a size of ;=0.05 I~m, the Si content in entire precipitates is <0.07% of the total rolled alloy weight, and the rolled alloy is grey or black on the anodized surface.
Crack g r o w t h in fighters t o be evaluated. Mater. Eval. Feb. 1992 50, (2), 277 Southwest Research Institute has recently developed a durability and damage tolerance (DADTA) program for Northrop F-5 fighters which will collect and analyse flight data on these aircraft m four countries. The data will help evaluate fatigue crack growth to update criteria for determination of airframe inspections and remaining fleet life. Esprit Technology will provide flight load data-recording systems to record dynamic structural loading over a 6-9 month period. Material coupons will also be evaluated in the laboratory to compare with field data.
The influence of test frequency, t e m p e r a t u r e , and environment on the fatigue resistance o f a Ni3AI-B/Cr/Zr intermatallic alloy. Camus, G.M.,
Duquette, D.J. and Stoloff, N.S. J. Mater. Res. Feb. 1992 7, (2), 313-320
Stress-controlled fatigue tests have been carried out on a Ni3AI-B/Cr/Zr alloy, at 600 and 800 °C in air and in vacuum at various test frequencies. Decreasing the test frequency and/or increasing the temperature leads to a decrease in the number of cycles to failure and a gradual disappearance of a fatigue fracture zone. This trend is shown to be related to a true creep component. Environment has a weak interacting effect on fatigue life but strongly influences the fracture path in the fatigue zones, with fracture becoming partly or entirely intergrenular when the environment is changed from vacuum to air. It is suggested that most of the fatigue life is spent in initiating a crack. Comparisons are made with some creep data in terms of fracture paths and time to rupture. Fatigue life at 800°C is shown to be entirely controlled by creep damage at the lowest test frequency at 0.2 Hz, Graphs, photomicrographs. 20 refs.
The influence of test frequency, temperature, and environment on the fatigue resistance o f a Ni3AI-B/Cr/Zr intermatallic alloy. Cereus, G.M.,
Duquette, D.J. and Stoloff, N.S. J. Mater. Res. Feb. 1992 7, (2), 313-320 Stress-controlled fatigue tests have been carried out on a Ni3AI-B/Cr/Zr alloy, at 600 and 800 °C in air and in vacuum at various test frequencies. Decreasing the test frequency and/or increasing the temperature leads to a decrease in the number of cycles to failure and a gradual disappearance of a fatigue fracture zone, This trend is shown to be related to s true creep component. Environment has a weak interacting effect on fatigue life but strongly influences the fracture path in the fatigue zones, with fracture becoming partly or entirely intergrenular when the environment is changed from vacuum to air. It is suggested that most of the fatigue life is spent in initiating a crack. Comparisons are made with some creep data in terms of fracture paths and time to rupture. Fatigue life at 800 °C is shown to be entirely controlled by creep damage at the lowest test frequency of 0.2 Hz. Graphs, photomicrographs. 20 refs.
Int J Fatigue January 1993
The d l e c t of p r o o f l o l l i n g on the M i g u e b e h a v i o r of open link chain.
Tipton, S.M. and Shoup, G.J. J. Eng. Mater. Technol. (Trans. ASME) Jan. 1992 114, (1), 27-33 Open link lifting chain (eg 8622H steel) is routinely proof loaded during manufacture. However, the effect of residual stresses imposed by thie operation on the fatigue strength of the chain has nut been quantitatively investigated. The results of constant amplitude fatigue teats on open link chain segments which If#re received proof loading at various levels are discussed. The chain was initially heat treated to relieve manufacturing residual stresses and then proof loaded at levels ranging from 0 to 82% of its break strength. Teats were performed at two different mean loads and four different load amplitudes. Failure site trends are noted as a function of applied loading and are correlated with results of a finite element stress analysis. Residual stresses are estimated using strains measured from strain gauges placed at critical locations on individual links during the proof load operations. Residual stress estimates are used with standard fatigue damage parameters to estimate the fatigue life of the chain and predictions are compared with data. Proof loading was shown to increase substantially the fatigue life of the chain. Residual stresses can explain the increase in fatigue life. Neuber's rule demonstrated the ability to model the data trends. Graphs. 10 refs. Influence of peak overload or variable loading sequences on fatiguecrack propagation in 18Cr-10Ni stainless steel. Brahmi, S. and Lehr, P. Mere. Etud. Sci. Rev. Metall. Dec. 1991 88, (12), 791-801 (in French) This work analyses the mfiuenca of isolated surcharges or charging modifications on the propagation of stress cracks in Z2CN18 10 stainless steel. The application of isolated surcharges or modifications in the intensity of charging leads to delayed effects that can be associated with the creation of an extended plastic deformation zone at the point of the crack. The model introduces a delay parameter CPi, defined as the relation of the speed effectively observed to the one theoretically foreseen by the law of matermal propagation. This parameter is correlated with a factor representative of the respective dimensions of the plaatified zone created at the bottom of the crack by the surcharge or the preceding charge and the actual plastified zone. Experimental results are compared with this model and discussed. Photomicrographs, graphs. 34 refs. Effect of stress ratio on fatigue crock growth in a t i t a n i u m eluminide alloy. Parida, B.K. and Nicholas, T. Int. J. Fract. Dec. 1991 52, (3), R51-R54 The matter of crack growth rate is developed mathematically. The stress intensity thereby corresponds to the load at which the crack opens fully during the loading part of the cycle. The resulting equation which expresses the driving force is, in terms of a quotient, to a power m. The value of m depends on the material under consideration. The material examined was Ti-24AI-11Nb intermatallic, Graphs. 6 refs. Fatigue analysis techniques f o r v i n t a g e steam t u r b i n e / g e n e r a t o r com-
ponents. Jhansale, H.R. and McCann, D.R.
Proc. Conf. Advances in Fatigue Lifetime Predictive Techniques, San Francisco, California, USA, 24 Apr. 1990 474-489
Some of the state-of-the-art engineering techniques utilized for the remaining life assessment and condition improvement of steam turbine/generator components in service are described. These include the finite element method for thermal and stress analyses, the inelastic strain-based fatigue analysis, and fracture mechanics for remaining life assessment. Special techniques for fabricating teat specimens from small samples and testing for current fatigue and fracture properties are also described (for 4130 steel). Fatigue lifetime m o n i t o r i n g in p o w e r plants. Riccardella, P.C., Deardorff, A.F. and Griesbach, T.J. Proc. Conf. Advances in Fatigue Lifetime Predictive Techniques, San Francisco, California, USA, 24 Apr. 1990 460-473 Metal fatigue is a potentially life-limiting mechanism for pressure-rataining components in nuclear and fossil-fuelled power plants. Fatigue cracking may occur at high stress locations due to the accumulation of startup-shutdown cycles and other thermal transients or load cycles during plant operation. This is accentuated in fossil power plants because of higher operating temperatures and the interaction between creep and fatigue effects. Under sponsorship of the Electric Power Rseeerch Institute (EPRI), an automated fatigue lifetime monitoring technology has been developed that utilizes plant processes data to perform a continuous prediction of fatigue damage accumulation in critical components. The methodology was demonstrated in two field tests at operating nuclear plants and has since been installed on a productmn basis in a number of plants. A demonstration fossil plant application has also been developed and mstalled, adding creep-fatigue damage and creckgrowth algorithms to the basic nuclear plant technology. The methodology has been incorporated into a PC-based computer program called FatiguePro. This program acquires plant process computer data (temperatures, pressures, flows, valve positions, etc.) and interprets them to predict local loads and temperatures m the monitored components. Green's functions are then used to determine transient thermal stresses at high stress locations in these components and to account for thermal history effects. A fatigue evaluation is then made, based on the computed transient stress history. The fatigue analysis, based on Miner's rule, is accomplished in accordance with ASME Boiler and Pressure Vessel Code stress and fatigue analysis procedures. Methodology is also available to perform fatigue and creep creck.growth analyses. The major benefit of on-line monitoring is that the actual challenge to structural integrity is measured, instead of simply counting designbasis cycles, as was the practice before the development of this system. Since actual plant operating cycles are typically less severe then those included in design, extension of predicted design lifetime can usually be obtained. Analytical and experimental
investigation o f fatigue in lap Joints.
Swenson, D.V., Chia, C.-C. and Derber, T.G. Proc. Conf. Advances in Fatigue Lifetime Predictive Techniques, San Francisco, California, USA, 24 Apr. 1990 449-459 A finite element model is presented that can simulate crack growth in layered structures such as lap joints. The layers can be joined either by rivets or adhesives. The crack is represented discretely in the mesh, and automatic remsehing is performed as the crack grows. Because of the connections between the layers, load
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High tamporaturo, l o w cycle f a t i g u e b e h e v l o u r o f AISI Type 316LN base metal, 316LN-316 w e l d j o i n t and 316 all-weld metal. Valsan, M., Sankara
Reo, K.B., Sandhya, R. and Mannan, S.L. Mater. Sci. Eng. A Jan. 1992 A14S, (2), L9-L12 Studies on the strein-controlled low cycle fatigue (LCF) behaviour of type 316LN stainless steel (SS) base material, type 316 SS all-weld metal and 316LN-316 weldments prepared by the shielded metal arc welding (SMAW) process at 837 K have been conducted at a strain rate of 3 x 10-3 s -1. The results indicated that the LCF resistance of all-weld metal was better than that of the base material while weldments displayed the least fatigue resistance. The better fatigue resistance of the all-weld metal has been attributed to the beneficial effects associated with fine distribution of ;~-ferrite in the auatenite matrix while the poor fatigue resistance of the weldment has been ascribed to the detrimental effects associated with coarse grain size and surface intergrenular cracking in the heet-affected zone. The cyclic stress amplitude varied with the material condition and strain amplitude in the LCF test. Graphs, photomicrographs. 9 refs.
Roiled a l u m i n l u m alloy adapted f o r superplaatic forming and method for making. Komatsubara, T., Tagata, 7". and Matsuo, M. UK Patent 2245592 8 Jan. 1992 Provided is a superplastic forming AI alloy in rolled form which exhibits superplaaticity and has improved corrosion resistance, weldability, and strength and fatigue property after auperplaatic forming, eliminating a need for heat treatment after superplaatic forming. Preferred alloys have an excellent outer appearance of grey to black colour after anodization. The alloy consists essentially of, in wt.%, 2.0-8.0% magnesium, 0.3-1.5% Mn, 0.0001-0.01% beryllium, an optional element selected from Cr, vanadium, and Zr, an optional grain refining agent of Ti or Ti and boron, <0.2% Fe and <0.1% Si as impurities, and the balance of AI, wherein intermatallic compounds have s size of up to 20 I~m, and the content of hydrogen present is up to 0.35 cm 3/100 g. Particularly when a minor amount of Ti or Ti and B grain refining agent is contained, Mn precipitates have a size of ;=0.05 I~m, the Si content in entire precipitates is <0.07% of the total rolled alloy weight, and the rolled alloy is grey or black on the anodized surface.
Crack g r o w t h in fighters t o be evaluated. Mater. Eval. Feb. 1992 50, (2), 277 Southwest Research Institute has recently developed a durability and damage tolerance (DADTA) program for Northrop F-5 fighters which will collect and analyse flight data on these aircraft m four countries. The data will help evaluate fatigue crack growth to update criteria for determination of airframe inspections and remaining fleet life. Esprit Technology will provide flight load data-recording systems to record dynamic structural loading over a 6-9 month period. Material coupons will also be evaluated in the laboratory to compare with field data.
The influence of test frequency, t e m p e r a t u r e , and environment on the fatigue resistance o f a Ni3AI-B/Cr/Zr intermatallic alloy. Camus, G.M.,
Duquette, D.J. and Stoloff, N.S. J. Mater. Res. Feb. 1992 7, (2), 313-320
Stress-controlled fatigue tests have been carried out on a Ni3AI-B/Cr/Zr alloy, at 600 and 800 °C in air and in vacuum at various test frequencies. Decreasing the test frequency and/or increasing the temperature leads to a decrease in the number of cycles to failure and a gradual disappearance of a fatigue fracture zone. This trend is shown to be related to a true creep component. Environment has a weak interacting effect on fatigue life but strongly influences the fracture path in the fatigue zones, with fracture becoming partly or entirely intergrenular when the environment is changed from vacuum to air. It is suggested that most of the fatigue life is spent in initiating a crack. Comparisons are made with some creep data in terms of fracture paths and time to rupture. Fatigue life at 800°C is shown to be entirely controlled by creep damage at the lowest test frequency at 0.2 Hz, Graphs, photomicrographs. 20 refs.
The influence of test frequency, temperature, and environment on the fatigue resistance o f a Ni3AI-B/Cr/Zr intermatallic alloy. Cereus, G.M.,
Duquette, D.J. and Stoloff, N.S. J. Mater. Res. Feb. 1992 7, (2), 313-320 Stress-controlled fatigue tests have been carried out on a Ni3AI-B/Cr/Zr alloy, at 600 and 800 °C in air and in vacuum at various test frequencies. Decreasing the test frequency and/or increasing the temperature leads to a decrease in the number of cycles to failure and a gradual disappearance of a fatigue fracture zone, This trend is shown to be related to s true creep component. Environment has a weak interacting effect on fatigue life but strongly influences the fracture path in the fatigue zones, with fracture becoming partly or entirely intergrenular when the environment is changed from vacuum to air. It is suggested that most of the fatigue life is spent in initiating a crack. Comparisons are made with some creep data in terms of fracture paths and time to rupture. Fatigue life at 800 °C is shown to be entirely controlled by creep damage at the lowest test frequency of 0.2 Hz. Graphs, photomicrographs. 20 refs.
Int J Fatigue January 1993
The d l e c t of p r o o f l o l l i n g on the M i g u e b e h a v i o r of open link chain.
Tipton, S.M. and Shoup, G.J. J. Eng. Mater. Technol. (Trans. ASME) Jan. 1992 114, (1), 27-33 Open link lifting chain (eg 8622H steel) is routinely proof loaded during manufacture. However, the effect of residual stresses imposed by thie operation on the fatigue strength of the chain has nut been quantitatively investigated. The results of constant amplitude fatigue teats on open link chain segments which If#re received proof loading at various levels are discussed. The chain was initially heat treated to relieve manufacturing residual stresses and then proof loaded at levels ranging from 0 to 82% of its break strength. Teats were performed at two different mean loads and four different load amplitudes. Failure site trends are noted as a function of applied loading and are correlated with results of a finite element stress analysis. Residual stresses are estimated using strains measured from strain gauges placed at critical locations on individual links during the proof load operations. Residual stress estimates are used with standard fatigue damage parameters to estimate the fatigue life of the chain and predictions are compared with data. Proof loading was shown to increase substantially the fatigue life of the chain. Residual stresses can explain the increase in fatigue life. Neuber's rule demonstrated the ability to model the data trends. Graphs. 10 refs. Influence of peak overload or variable loading sequences on fatiguecrack propagation in 18Cr-10Ni stainless steel. Brahmi, S. and Lehr, P. Mere. Etud. Sci. Rev. Metall. Dec. 1991 88, (12), 791-801 (in French) This work analyses the mfiuenca of isolated surcharges or charging modifications on the propagation of stress cracks in Z2CN18 10 stainless steel. The application of isolated surcharges or modifications in the intensity of charging leads to delayed effects that can be associated with the creation of an extended plastic deformation zone at the point of the crack. The model introduces a delay parameter CPi, defined as the relation of the speed effectively observed to the one theoretically foreseen by the law of matermal propagation. This parameter is correlated with a factor representative of the respective dimensions of the plaatified zone created at the bottom of the crack by the surcharge or the preceding charge and the actual plastified zone. Experimental results are compared with this model and discussed. Photomicrographs, graphs. 34 refs. Effect of stress ratio on fatigue crock growth in a t i t a n i u m eluminide alloy. Parida, B.K. and Nicholas, T. Int. J. Fract. Dec. 1991 52, (3), R51-R54 The matter of crack growth rate is developed mathematically. The stress intensity thereby corresponds to the load at which the crack opens fully during the loading part of the cycle. The resulting equation which expresses the driving force is, in terms of a quotient, to a power m. The value of m depends on the material under consideration. The material examined was Ti-24AI-11Nb intermatallic, Graphs. 6 refs. Fatigue analysis techniques f o r v i n t a g e steam t u r b i n e / g e n e r a t o r com-
ponents. Jhansale, H.R. and McCann, D.R.
Proc. Conf. Advances in Fatigue Lifetime Predictive Techniques, San Francisco, California, USA, 24 Apr. 1990 474-489
Some of the state-of-the-art engineering techniques utilized for the remaining life assessment and condition improvement of steam turbine/generator components in service are described. These include the finite element method for thermal and stress analyses, the inelastic strain-based fatigue analysis, and fracture mechanics for remaining life assessment. Special techniques for fabricating teat specimens from small samples and testing for current fatigue and fracture properties are also described (for 4130 steel). Fatigue lifetime m o n i t o r i n g in p o w e r plants. Riccardella, P.C., Deardorff, A.F. and Griesbach, T.J. Proc. Conf. Advances in Fatigue Lifetime Predictive Techniques, San Francisco, California, USA, 24 Apr. 1990 460-473 Metal fatigue is a potentially life-limiting mechanism for pressure-rataining components in nuclear and fossil-fuelled power plants. Fatigue cracking may occur at high stress locations due to the accumulation of startup-shutdown cycles and other thermal transients or load cycles during plant operation. This is accentuated in fossil power plants because of higher operating temperatures and the interaction between creep and fatigue effects. Under sponsorship of the Electric Power Rseeerch Institute (EPRI), an automated fatigue lifetime monitoring technology has been developed that utilizes plant processes data to perform a continuous prediction of fatigue damage accumulation in critical components. The methodology was demonstrated in two field tests at operating nuclear plants and has since been installed on a productmn basis in a number of plants. A demonstration fossil plant application has also been developed and mstalled, adding creep-fatigue damage and creckgrowth algorithms to the basic nuclear plant technology. The methodology has been incorporated into a PC-based computer program called FatiguePro. This program acquires plant process computer data (temperatures, pressures, flows, valve positions, etc.) and interprets them to predict local loads and temperatures m the monitored components. Green's functions are then used to determine transient thermal stresses at high stress locations in these components and to account for thermal history effects. A fatigue evaluation is then made, based on the computed transient stress history. The fatigue analysis, based on Miner's rule, is accomplished in accordance with ASME Boiler and Pressure Vessel Code stress and fatigue analysis procedures. Methodology is also available to perform fatigue and creep creck.growth analyses. The major benefit of on-line monitoring is that the actual challenge to structural integrity is measured, instead of simply counting designbasis cycles, as was the practice before the development of this system. Since actual plant operating cycles are typically less severe then those included in design, extension of predicted design lifetime can usually be obtained. Analytical and experimental
investigation o f fatigue in lap Joints.
Swenson, D.V., Chia, C.-C. and Derber, T.G. Proc. Conf. Advances in Fatigue Lifetime Predictive Techniques, San Francisco, California, USA, 24 Apr. 1990 449-459 A finite element model is presented that can simulate crack growth in layered structures such as lap joints. The layers can be joined either by rivets or adhesives. The crack is represented discretely in the mesh, and automatic remsehing is performed as the crack grows. Because of the connections between the layers, load
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